1. Field of the Invention
The present invention relates to rollers such as a contact roller (pressure roller) or a nip roller used in web winding devices or devices for film sheets, and more particularly to a bend adjustable roller.
2. Description of the Related Art
With an increase in the width of web materials, the shaft of a contact roller used in web winding devices is made longer. The contact roller has the ratio of the length of the shaft to the diameter of the contact roller has recently taken a value from 15 to 30. This leads us to an undesirable phenomenon that the contact roller bends in an arch-like form between bearings on both ends in a direction away from the winding shaft of a web winding device, even though with high stiffness or light weight. Accordingly, on the shaft of the contact roller nip pressure is less at its center than at its ends. This results in forming sheets with winding wrinkle, winding knob, or winding slippage with low quality.
Japanese Patent Laid-Open No. H6-39300 discloses a contact roller device that is capable of adjusting bending amount to be applied on the contact roller. The device has a pair of control shafts, a plurality of roller bearings (ball bearings), each bearing supporting an end area of each control shaft; and movable frames which hold the roller bearings. The roller bearings are aligned in the axial direction of each control shaft. Pushing the movable frames in a horizontal direction with cylinder devices gives bending force on one end of each control shaft to bend the contact roller.
However, this requires the large force of the cylinder devices because the contact roller device has a limitation on the length between the roller bearings aligned in the axial direction due to its mechanical structure. Accordingly, the large force is required to obtain a predetermined amount of bending.
Such large force makes the life of the roller bearings shortened and the rotation loss of the roller increased.
Moreover, the roller bearings and the movable frames holding the roller bearings receive the reaction force of the bending force. Since in general there is provided a shift frame for shifting the contact roller in backward depending on winding-slack amount with the swing mechanism, the contact roller cannot receive large force. Even so, taking this method makes a winding slack adjusting mechanism and a swing mechanism large and complicated.